1. Field of the Invention
The present invention relates to methods and apparatus for grinding a surface of a workpiece to a super-finish surface with micro oil pockets by grinding the workpiece surface with a super-finish grinding wheel after a finish grinding with a finish grinding wheel.
2. Description of the Related Art
Heretofore, crankpins and journals of crankshafts have been ground with a finish grinding wheel on a grinding machine and then, have been lapped on a lapping machine for improved surface roughness. The surfaces of the crankpins and journals after the lapping process have a roughness of the order which ranges from 0.4 through 0.8 μmRzISO. As shown in FIG. 1, the section curve representing the roughness in an exaggerated scale shows that the lapped surface is shallow and uniform in the height of irregularity and that there hardly exist micro oil pockets. Due to lack of micro oil pockets, such lapped surfaces of the crankpins and journals are liable to suffer from seizure to bearing members therefor.
To obviate this drawback, it is desirable that the crankpins and journals be ground so that as shown in FIG. 2, the section curve representing the surface roughness thereof has the irregularity which is uniform in the height of peaks and roughly uniform in the depth of bottoms, but which disperses deep bottoms here and there to provide micro oil pockets. Further, since the crankpins and journals are ground on a grinding machine and then, are lapped on a lapping machine, a longer machining time as well as a higher cost for the machining facilities are disadvantageously unavoidable.